Amiga recapping is something that needs to be done it’s as simple as that, just like your car or gas boiler needs a service and certain parts that need replacing. When Commodore created the Amiga family of computers and consoles (in fact any manufacture) never envisaged that the Amiga computer will still be actively used in 2019.
The design and manufacturing was to be made as cheap as possible so there was no serious thought on the quality of components that was used. They were fit for purpose but the issue in particular are the surface mount capacitors.
These SMD capacitors in the Amiga are electrolytic which in fact have a liquid inside called electrolyte however with age (even if the Amiga is not used) these will start to leak. Now it’s not always easy to see the leakage as sometimes the leak is under the capacitor itself, and you won’t see it, but the majority of the time there can be visible clues, for example the solder is dull and has a green tinge to it, or simply the capacitor falls off!